1. Field of the Invention
The present invention relates to a printed circuit board, suitable for the attachment of an electric or electronic component (for instance, a BGA component), and a semi-conductor apparatus including such a printed circuit board and such a component.
2. Description of the Related Art
Currently, various types of printed circuit boards are used. A multiple-layered printed circuit board comprises a plurality of insulator layers and a plurality of conductor layers (for instance, six to eight signal pattern layers). An outermost conductor layer has a plurality of foot patterns for attachment of an electric or electronic component and signal patterns extending from those foot patterns. The signal pattern that is pulled out from the foot pattern for a BGA component is pulled out for wiring such that the pattern has a certain uniform pattern width except for a power supply wire and a ground wire.
The BGA stands for Ball Grid Array and describes a chip having small spherical solder terminals arranged on the back thereof (in many cases arranged in a grid-like fashion). When this BGA chip (or a BGA component) is placed on a substrate and is heated by applying infrared thereto, the spherical solder terminals thereof are fused to join with terminals of the substrate. In other words, the BGA chip is surface mounted to the substrate. Since the BGA terminals can be disposed on the entirety of the back of the chip or component, the distance between the terminals of the chip or component can be formed relatively greater. In addition, with BGA, there is provided an advantage in which a package for the chip or component can be made compact even if the chip or component has a number of terminals.
The insulator layers are formed from a glass cloth material or a resin material, and the outermost conductor layer is protected with a solder resist. The solder resist covers signal patterns of the outermost conductor layer and has openings for permitting foot patterns to be exposed. A BGA component, which is an electric or electronic component to be mounted to a printed circuit board, has solder balls and these solder balls are connected to the foot patterns of the printed circuit board through the openings of the solder resist.
A printed circuit board which is highly durable and reliable has a plurality of insulator layers formed from a glass cloth material. Most insulator layers are formed from a glass cloth material, but an insulator layer positioned directly underneath a conductor layer including foot patterns is not formed from a glass cloth material but from a resin material, and a printed circuit board including such an insulator layer formed from a resin material is called and known as a built-up substrate. When compared with a printed circuit board in which all the insulator layers thereof are formed from a glass cloth material, the built-up substrate is lighter in weight and suitable for use in a semi-conductor apparatus such as a portable information apparatus or the like.
A number of electric or electronic components are mounted to a printed circuit board. In particular, a BGA component has solder bumps or solder balls, and is attached to the printed circuit board through the reflow of the solder thereof. The printed circuit board is subjected to stress due to thermal expansion at the time of reflow and mechanical stress (external stress) generated during an electrical test after the components are mounted or when the printed circuit board is built into an apparatus. It sometimes happens that stress is concentrated on a portion of the printed circuit board where the BGA component is positioned. The BGA component is relatively large in external size and is more rigid than the printed circuit board. In addition, a small foot pattern is used to join the BGA component to the printed circuit board.
When stress is applied to the printed circuit board, the printed circuit board deforms relative to the printed circuit board, or the BGA component deforms relative to the printed circuit board. When the printed circuit board and the BGA component deform relative to each other, stress tends to be easily applied to the foot patterns, in particular, the foot pattern in an external row and a signal pattern extending the foot pattern.
An insulator layer formed using no glass cloth material has a mechanical strength lower than that of an insulator layer formed using a glass cloth material, and therefore the former is liable to deform. When a certain stress is applied to a foot pattern and a signal pattern in an outer row, an insulator positioned underneath them is also subjected to the stress locally and liable to deform. Due to this, the signal pattern extending from the foot pattern in the outer row is liable to deform and therefore break. In addition, an insulator formed from a resin material tends to be easily damaged.
Moreover, the aforesaid problem happens even when another type of LSI packaged electronic component is used.
For instance, it happens even when a PGA (Pin Grid Array in which pin-type terminals are arranged on the back of a semi-conductor in a two-dimensional fashion) or the like is mounted on a printed circuit board. In addition, the problem happens in not only a multiple-layered printed circuit board but also a single-layered one. Moreover, the problem happens even when a pin-type terminal such as a PGA is inserted and mounted. Furthermore, assuming that a PGA terminal or the like (typically, a pin-like terminal) is surface mounted on a foot pattern, the problem may happen.
An object of the present invention is to provide a printed circuit board and a semiconductor apparatus which is constructed such that a signal pattern extending from a foot pattern is difficult to break even when a stress is applied to the printed circuit board and a component thereon.
With a view to attaining the above object, the present invention provides a printed circuit board having a plurality of connecting portions for connection to terminals of a component and signal patterns extending from the connecting portions, the connecting portions including outer connecting portions and inner connecting portions, wherein the width of at least a part of the signal pattern extending from the outer connecting portion is greater than the width of the signal pattern extending from the inner connecting portion.
The present invention also provides a printed circuit board having a plurality of foot patterns for attachment of a component and signal patterns extending from the foot patterns, the foot patterns including outer foot patterns and inner foot patterns, wherein the width of at least a part of the signal pattern extending from the outer foot pattern is greater than the width of the signal pattern extending from the inner foot pattern.
The present invention further provides a printed circuit board, wherein the width of the signal pattern extending from the outer foot pattern is constant along the length thereof.
The present invention also provides a printed circuit board, wherein the signal pattern extending from the outer foot pattern has a first portion a predetermined distance distant from a connection position between the foot pattern and the signal pattern and a second portion connected to the first portion, wherein the width of the first portion of the signal pattern is greater than the width of the second portion of the signal pattern.
The present invention further provides a printed circuit board further including a plurality of insulator layers and a plurality of conductor layers, wherein an outermost layer of the conductor layers includes the foot patterns for attachment of a component.
The present invention also provides a printed circuit board, wherein the insulator layers include a first insulator layer positioned directly underneath the outermost layer and a second insulator layer positioned inwardly of the first insulator layer, the first insulator layer being formed using a resin material, the second insulator layer being formed using a glass cloth material.
The present invention further provides a semiconductor apparatus comprising a printed circuit board, and a component mounted to the printed circuit board, wherein the printed circuit board has a plurality of foot patterns for attachment of a component and signal patterns extending from the foot patterns, wherein the foot patterns include outer foot patterns and inner foot patterns, and wherein the width of at least a part of the signal pattern extending from the outer foot pattern is greater than the width of the signal pattern extending from the inner foot pattern.
According to the above construction, the width of the signal pattern extending from the foot pattern in the outer row located at a position where a deformation is liable to happen when a stress is applied thereto is made greater than the width of the foot pattern in the inner row where a deformation is difficult to happen even when a stress is applied thereto, whereby the signal pattern located at the position where a deformation is liable to happen is constructed so as to be free from deformation.